linux-kernel - Re: [PATCH v5 16/18] perf: enable reading of perf.data files from different ABI rev

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Date:	Tue, 07 Feb 2012 10:57:36 -0700
From:	David Ahern <dsahern@...il.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...e.hu,
	acme@...hat.com, robert.richter@....com, ming.m.lin@...el.com,
	andi@...stfloor.org, asharma@...com, ravitillo@....gov,
	vweaver1@...s.utk.edu, khandual@...ux.vnet.ibm.com
Subject: Re: [PATCH v5 16/18] perf: enable reading of perf.data files from
 different ABI rev



On 02/07/2012 10:42 AM, Stephane Eranian wrote:
>>> Well, the current code solves the problem once and for all. Old tools
>>> can still read new files and vice-versa. If you think that's a problem I
>>> can simply bail out if sz > our_sz.
>>
>> My sensitivity on this is when endianness is broken it is a nightmare to
>> find. You end up lacing the code with printfs trying to find which size
>> field is going off the charts making the parsing of the file fail - or
>> worse the sizes are slightly off and you get non-sense out.
>>
>> New commands should be able to read old files; old commands reading new
>> files is a bit of a stretch in that the code has to be future-proofed.
>> It seems like a reasonable requirement for data files to be examined by
>> a command of the same vintage or newer as the command that wrote the file.
>>
> Fine then, I can simply strip that part of the code and return an
> error is sz > our_sz.
> How about that?


That's my preference - with a nice grep-able error message about an
unexpected attr size.

David
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